In light of the scarcity of natural resources and the increasing impact of CO2 on the environment, the current trend in automotive engineering is to use hybrid drive systems, which store the electric energy generated in braking modes and recover drive energy from the stored energy to provide assistance to the vehicle for the drive mode and, in particular, for accelerating processes. This strategy offers the possibility of decreasing the drive power of the internal combustion engine, which serves as the primary drive, for comparable road performance. The result of such “downsizing” is not only a reduction in the fuel consumption, but it also raises the possibility of assigning the vehicles concerned to a lower emissions class that satisfies a lower-cost road tax category.
These goals are not limited to electric motor powered hybrids, but used for hydrostatic hybrid systems owing to the high energy density of hydraulic systems. Such a hydrostatic drive system with recovery of the braking energy is disclosed, for example, in DE 10 2005 060 994 A1.
The operational performance of such a hydrostatic hybrid system can be optimized by using a dual piston accumulator, instead of a high pressure hydraulic accumulator and a separate low pressure hydraulic accumulator. This approach permits the design to be more compact, as compared to a design using separate accumulators. In addition to compactness, the current trend is to reduce the structural weight as much as possible for systems that are installed into vehicles. Dual piston accumulators of the conventional design type, as described, for example, in U.S. Pat. No. 6,202,753 B1 for use in deep water drilling operations, do not meet these requirements.